The present invention relates to an air purification-functioning road and a method for purifying polluted air over roads.
Exhaust gases emitted from vehicles contain a large amount of pollutants such as nitrogen oxides (NOx), etc., polluting the atmospheric air.
In these days calling for protection of the global environment, it is most desirable to purify such polluted air.
In this connection, catalytic air purification apparatuses have been so far proposed.
However, mere provision of such catalytic air purification apparatuses in heavy air pollution areas has had a space problem and also a problem of spoiling the road appearance and thus has been hard to realize.
Available surface areas of roads such as pedestrian sidewalks, car running roadways, etc. are so large that it has been regarded as ideal to utilize such larger road surfaces for purification of the polluted air and particularly more desirable from the viewpoint of diffusion prevention of polluted air, if the polluted air over car running roadways can be carried out.
Photocatalysts capable of causing a photocatalytic reaction to take place even at the ordinary temperature when exposed to light such as titanium dioxide (TiO2), etc. are now attracting considerable attention. It is known that pollutants such as nitrogen oxides, etc. are converted by the photocatalytic reaction caused by the photocatalysts when exposed to light and the converted matters are retained on the catalysts and removed therefrom by water washing.
The present invention is based on a large available surface areas of roads and a photocatalyst such as a titanium dioxide, and is directed to a road capable of purifying polluted air without any space problem or problem of spoiling the road appearance and also to a method for purifying polluted air over the road.
In order to attain the above object, the present invention provides an air purification-functioning road, in which a photocatalyst layer comprising a photocatalyst such as titanium dioxide, etc. and a retainer material for retaining the photocatalyst being fixed to the surface of the road by a fixer material and at least one part, preferably the whole of the surface of the road being covered by the photocatalyst layer. The retainer material and the fixer material can be made from the same material.
Preferably, the road is provided with a dewaterable pavement and the photocatalyst layer is water-permeable and formed on the dewaterable pavement. The dewaterable pavement is not particularly limited thereto and can include those as will be described later.
According to one embodiment of the present invention, the photocatalyst layer comprises a photocatalyst, cement, a filler and water, where the cement can serve as the retainer material and the fixer material at the same time.
According to another embodiment of the present invention, the photocatalyst layer comprises a photocatalyst and an inorganic paint, where the inorganic paint can serve as the retainer material and the fixer material at the same time.
According to other embodiment of the present invention, the photocatalyst layer is a sheet comprising a photocatalyst and a fluororesin, where the fluororesin can serve as the retainer material and the fixer material at the same time.
In order to attain aforementioned object, the present invention provides a method for purifying polluted air over roads, which comprises fixing a photocatalyst layer comprising a photocatalyst such as titanium oxide, etc. and a retainer material for retaining the photocatalyst to at least one part, preferably the whole of a road surface by a fixer material, thereby covering the part or the whole of the road surface, purifying pollutants in exhaust gases emitted from vehicles by photocatalytic reaction of the photocatalyst and sprinkling water onto the road surface, thereby washing away pollutant-originating matters as retained on the photocatalyst layer.
Preferably, the road is provided with a dewaterable pavement, and the photocatalyst layer is water-permeable and is formed on the dewaterable pavement.
It is preferable to periodically sprinkle water in accordance with the degree of pollution.
According to one embodiment of the present invention, the photocatalyst layer is formed by injecting or spraying a mixture comprising a photocatalyst, cement, a filler and water onto the road surface, where the cement serves as the retainer material and the fixer material at the same time.
According to another embodiment of the present invention, the photocatalyst bed is also formed by injecting or spraying a mixture comprising a photocatalyst and an inorganic paint onto the road surface, where the inorganic paint serves as the retainer material and the fixer material at the same time.
In the present invention, it is preferable that the road is for vehicle use only and water sprinkling is carried out from the center line towards both sides in the width direction of the road.
In the present invention, the photocatalyst causes photocatalytic reaction to take place when exposed to sun light, purifying polluted air by the photocatalytic reaction.
Photocatalyst is a substance capable of causing a photocatalytic reaction to take place, when irradiated with light with a wavelength of energy corresponding to its band gap or higher. The photocatalyst for use in the present invention includes at least one of metal compound semiconductors such as titanium dioxide, zinc oxide, tungsten oxide, iron oxide, strontium titanate, bismuth oxide, molybdenum sulfide, cadmium sulfide, etc. At least one of metals such as copper, silver, gold, lanthanum, cerium, zinc, vanadium, iron, cobalt, nickel, ruthenium, rhodium, palladium, platinum, etc. or their metal compounds can be added to the surfaces and/or insides of particles of the metal compound semiconductor. In the present invention titanium dioxide is particularly preferable from the viewpoint of its distinguished photocatalytic reaction.
xe2x80x9cTitanium dioxidexe2x80x9d includes so called hydrous titanium oxide, hydrated titanium oxide, metatitanic acid, orthotitanic acid and titanium hydroxide besides the titanium dioxide, and also includes titanium dioxide containing at least one of metals such as copper, silver, gold, lanthanum, cerium, zinc, vanadium, iron, cobalt, nickel, ruthenium, rhodium, palladium, platinum, etc. or their metal compounds added to the surfaces and/or insides of particles of the titanium dioxide. Addition of at least one of the metals or their metal compounds to the surfaces and/or insides is preferable from the viewpoint of the distinguished photocatalytic reaction. Titanium dioxide containing at least one of such metals as gold, lanthanum, iron, ruthenium, rhodium, palladium and platinum or their meal compounds as added to the surfaces and/or insides of particles of titanium dioxide is particularly preferable.
Atmospheric air pollutants include, for example, nitrogen oxides (NOx), sulfur compounds such as sulfur oxides (SOx), hydrogen sulfide, etc. carbon monoxide, hydrocarbons (HC), etc., as contained in exhaust gases emitted from vehicles, and also include air pollutants and also foul-smelling matters as emitted from factories, livestock farms, refuse incineration plants, dumping grounds, etc. Nitrogen oxides (NOx) and sulfur oxides (SOx) are converted to nitric acid and sulfuric acid, respectively, by photocatalytic reaction of the photocatalyst layer and retained on the photocatalyst layer, whereas carbon monoxide is converted to carbon dioxide and is toxically abated thereby. Many other pollutants are also decomposed by the photocatalytic reaction.
The pollutants retained on the photocatalyst layer are washed away from the photocatalyst layer by rain water during raining or by artificially sprinkled water, while the photocatalyst layer can be brought into an activated state of photocatalytic reaction again.
That is, mere provision of a photocatalytic layer on the surface of the existing dewaterable pavement can purify polluted air through contact with the photocatalytic layer on the road surface and prevent diffusion of the polluted air. There is not any space problem or road appearance problem.
Furthermore, owing to the broad road surface by nature and also to numerous fine projections and depressions formed on the dewaterable pavement surface, as will be described later, the surface area of the photocatalyst layer can be much more increased and purification of polluted air by the photocatalyst layer can be effectively carried out.
Even if the photocatalyst layer on the dewaterable pavement surface is worn out by running of vehicles, there still remains the photocatalyst layer in the numerous fine depressions formed between the adjacent projections. The remaining photocatalyt layer in the depressions can compensate for the worn-out photocatalyst.